The last several years has seen an increasing emphasis being placed on the design of engines to make them more compact, lighter and yet with improved fuel economy, efficiency, reduced emissions, greater service life and increased power output per cylinder. As present day engines are converted or upgraded, the piston assembly is subject to even higher combustion chamber pressures and temperatures.
Attempts have been made to overcome the effects of higher combustion chamber pressures by altering the design of the piston member and its associated components such as the piston pin and the retaining device relative to the piston member. An example is disclosed in U.K. Pat. Application No. GB 2,225,087 published May 23, 1990 to Applicant Metal Leve S. A. Industria E Comerclo. The publication discloses an articulated piston assembly comprised of a head having a pair of pin bosses, a skirt portion and a wrist pin mounted in the bosses and the skirt portion. The assembly further includes a restraining member to prevent lateral deformation of the pin bosses. The bosses are split and are clamped to the pin by means of nuts and bolts. Thus, the pin is prevented from axial movement. Furthermore, the restraining members are in contact with the pin bosses along their entire axial length.
Another example of a piston assembly is disclosed in U.K. Pat. Application 0,222,359 published May 20, 1887 to Applicant AE PLC. The publication discloses an articulated piston assembly comprised of a crown portion having gudgeon-pin bosses, a skirt portion and a gudgeon-pin. A pair of stub-pins are fixedly positioned in the crown portion and prevent axial movement of the gudgeon-pin. The stub-pins are comprised of a plastic material. Furthermore, the stub-pins are in contact with the pin bosses along their entire axial length.
Another example of a piston assembly is disclosed in U.S. Pat. No. 2,797,135 issued Jun. 25, 1957 to J. E. Johansson. The patent discloses a piston assembly comprised of a piston and a tubular gudgeon pin. The pin is retained within the piston by two expansion members consisting of a material having a coefficient of expansion greater than the pin and preferably equal to or greater than the coefficient of expansion of the piston. In this patent the expansion members are positioned within the cylindrical pin. A fastening device axially fixedly positions the pin within the piston. Furthermore, the expansion members are in contact with the cylindrical pin along their entire axial length.
Another example of a piston assembly is disclosed in "Overhaul Manual AVCO Lycoming Direct Drive Engine", the publication is the fifth printing Part No. 60294-7 and is dated in December of 1974. AVCO's Lycoming Division is located in Williamsport, Pa. 17701. The manual on page 1-12 discloses a cylinder, piston and valve components. The pin within the piston assembly is retained in place by a plug positioned in the piston bore similar to the above publication. As shown in the optional example, the plug could be positioned within the cylindrical pin. However, as disclosed the head of the plug is quite long and reduces the surface area between the pin and the piston resulting in high loads being transmitted between the corresponding surface areas of the pin and the piston. Furthermore, the plugs are in contact with the cylindrical pin along their entire axial length.
Another example of a retainer is disclosed in U.S. Pat. No. 1,923,717 issued on Aug. 22, 1933 to Fritjof Frelin. A pair of plugs are threaded onto opposite ends of a sleeve and each has an expandable ring positioned therein contacting and sealing against the surface of a bore through a wrist pin. The head or flange of each plug is larger than the outer diameter of the wrist pin and contacts the piston, thus retaining the wrist pin therebetween. This structure does not permit preassembly of the plugs and wrist pin which can only be assembled at the time of assembling the piston, rod, wrist pin and plugs. Furthermore, the process required to assemble the above components is time consuming, increases cost and increases the total number of parts to be assembled.
In a portion of the above listed publications the restraining members and the stub-pins are positioned within the piston bore through which the gudgeon pin is positioned. In these applications, the surface area of the piston bore is shared by the surface area of the gudgeon pin and the surface area of the restraining members or the stub-pins. Thus, resulting in a higher load being applied to the piston bore surface area and the gudgeon pin surface area. The above listed U.S. patent and the optional example of the manual discloses that expansion members are or can be positioned within the cylindrical pin. Furthermore, most of the disclosures have the retaining members and stub-pins in contact with the mating part along its entire axial length.
The present invention is directed to overcome one or more of the problems as set forth above.